In the manufacture of catalytic converters used to eliminate the undesirable constituents in combustion engine exhaust gases, it is currently common practice as an alternative to bedded ceramic beads to employ a ceramic monolith or substrate that is coated with a catalyst and contained in a sheet metal housing through which the exhaust gases are directed. The ceramic is both frangible and has a much lower coefficient of expansion than the sheet metal forming the housing and as a result, an arrangement is required that will both support and maintain sealed integrity of the ceramic monolith without fracture thereof in the harsh vibratory and temperature environment of the engine exhaust system. Moreover, the ceramic monolith is normally formed by extrusion through a die and as a result a new die is required for every cross-sectional change.
Honeycomb substrates formed of foil strips have been proposed in avoidance of such problems; however, they are typically deficient in some respect and/or present their own problems from a manufacturing and/or functional standpoint. For example, it is known to form the honeycomb substrate by spirally winding strips of smooth and corrugated foil but there results the problem of relative telescoping or sliding between the layers which abrades the catalyst. With such an arrangement, it is difficult to maintain the integrity of the metal substrate without some form of mechanical strengthening or bonding of the layers. Then there remains another major problem of allowing design flexibility in the shape of the metal layered substrate cross-section to meet various space allocations while maintaining a curved profile for housing strength reasons. This is particularly important in meeting certain vehicle underflow space requirements where a low profile cross-section of for example oval shape is desired over a circular one which requires a larger height for the same area. Moreover, there is the difficulty and expense of manufacture in completely forming a metal layered substrate so as to be suitable for a final step of applying the catalyst coating. For example, a whisker-covered metal foil has been developed that is ideally suited to retain a catalyst coating as disclosed in U.S. Pat. Nos. 4,318,828 and 4,331,631 assigned to the assignee of the present invention. However, the whiskers on such foil are metal oxide growths and as a result, form both a metallurgical and mechanical barrier preventing intimate contact between the base metal of adjacent layers of the foil and thereby their strong fusion welding which is normally necessary to form a suitable honeycomb substrate for the catalyst.